1. Field of the Invention
The present invention relates to the time-slot assigning technologies, and it particularly relates to a method for assigning time slots in terminal apparatus to be communicated and also particularly relates to a base station apparatus using said method.
2. Description of the Related Art
In wireless communications, the effective utilization of frequency resources is generally desired. Such needs are all the more growing with the broader use of cellular phone system and second-generation cordless telephone system. One of the technologies meeting such needs is spatial multiplexing. Spatial multiplexing is a technology for communicating with a plurality of terminal apparatuses using the same frequency and the same timing by adjusting the directional pattern of the antennas. In such a spatial multiplexing scheme, signals for a plurality of terminal apparatuses are separated by the directivity pattern of the antennas. And adaptive array antenna technology is used in forming such a directivity pattern.
Generally speaking, adaptive array antenna technology is subject to deterioration of communication quality in two cases as mentioned below due to an insufficient separation among signals for a plurality of terminal apparatuses by an antenna directivity pattern. The first of the cases is where at least two of the terminal apparatuses exist roughly in the same direction. In this case, it becomes difficult to separate signals for the two terminal apparatuses by a difference in the directional pattern. The second of the cases is where the strength ratio between the received signals from at least two of the terminal apparatuses is large to a certain degree. In this case, it becomes difficult to separate signals for the two because the signal strength ratio between the two is larger than the gain ratio of the antennas (See Reference (1) in the following Related Art List, for instance).